1. Field of the Invention
The present invention relates to a thin film magnetic recording medium and a method of producing the same.
2. Description of the Prior Art
Nowadays, in a magnetic recording apparatus, the improvement of the recording density of magnetic recording media has been considered as the most important technical subject. The main parameters for improving the recording density of recording media are the coercive force Hc, the residual magnetic flux Br, and the magnetic layer thickness.
There is the following relation among those parameters and electromagnetic characteristics. EQU W.alpha.(Br/Hc ).sup..beta...delta..alpha. EQU E.alpha.Br.(Hc/Br).sup..beta...delta..alpha. EQU .alpha.=0.85-0.50 EQU .beta.=0.15-0.50
where W and E represet the width of a reproduced waveform and the reproducing output of a magnetic head respectively.
According to the above-mentioned relation, it is understood that in order to improve the recording density of a magnetic recording medium, it is necessary to make the waveform width W small while suppressing the lowering of the reproducing output E as small as possible.
In order to make the waveform width W small, it is necessary to make both the ratio (Br/Hc) and the magnetic layer thickness .delta. small. At that time, in order to prevent the lowering of the reproducing output E, it is desirable to make the product of the residual flux Br and the magnetic layer thickness .delta. larger, and particularly in a thin film magnetic recording medium, it is desirable to make the magnetic layer thickness .delta. small while making the residual flux Br as well as the coercive force Hc large. On the basis of this point of view, conventional, magnetic recording media such as magnetic disks, and the like, have been manufactured.
A trial for making the coercive force Hc large has been performed in order to make the recording density higher in thin film magnetic recording media. In such a trial, however, if the coercive force Hc is to be made large, the magnetic layer thickness .delta. is required to be small, resulting in a problem that the magnetic layer thickness becomes uneven. There is a further problem that making the magnetic layer thickness .delta. small may casue reduction in the reproducing output E unless the residual flux Br is made large.
A cause of the fact that the coercive force Hc becomes small when the magnetic layer thickness .delta. is large is considered to exist in the crystal structure of the cobalt material such as cobalt phosphorus or the like forming the magnetic layer. That is, a change in grain size D of a crystal l such as cobalt phosphorus, or the like, in the growing process thereof, as shown in FIG.5, is considered as a cause of the above mentioned fact. As shown in FIG.6, it is considered that the smaller the grain size D is the higher the coercive force Hc is made unless the grain becomes amorphous. That is, it is considered that the crystal structure has the maximum coercive force Hc when the grain size D is about 50 A.